Use generics for Add and Delete Methods

atom.go

@@ -1,6 +1,7 @@
 package atom
 
 import (
+	"encoding/xml"
 	"fmt"
 	"html"
 	"mime"
@@ -11,6 +12,29 @@ import (
 	"golang.org/x/text/language"
 )
 
+type Countable interface {
+	*xml.Attr | *Person | *Category | *Link | *ExtensionElement | *Entry
+}
+
+func addToSlice[C Countable](slice []C, countable C) {
+	if slice == nil {
+		slice = make([]C, 1)
+		slice[0] = countable
+	} else {
+		slice = append(slice, countable)
+	}
+}
+
+func deleteFromSlice[C Countable](slice []C, id int) error {
+	length := len(slice)
+	if id > length {
+		return fmt.Errorf("id %v out of range %v", id, length)
+	}
+
+	slice = append(slice[:id], slice[id+1:]...)
+	return nil
+}
+
 // isValidIRI checks whether an IRI is valid or not. It returns a bool.
 // https://www.w3.org/2011/04/XMLSchema/TypeLibrary-IRI-RFC3987.xsd
 func isValidIRI(iri string) bool {